The effect of process parameters including water rate 2. 54 ~3. 16 m

3

/h

gas rate 0. 037 ~ 0.110 m

3

/h

slide gate opening degree (51% ~ 100% ) and nozzle submerged depth 78 ~ 108 mm on gas ratio distribution at wide side of mold for slab casting with nozzle argon blowing has been analyzed by an established 108 mm x 420 mm water model with geometry similarity ratio 6 ：10 to simulate 180 mm x 700 mm mold for slab casting and using digital image process technique. Results show that with water rate- 3. 16 m

3

/h ( corresponding original type 1. 50 m

3

/h)

gas rate- 0. 037 m

3

/h (original type 0. 120 m

3

/h)

nozzle bottom being concave shape

slide g

ate opening degree- 51% and submerged depth of nozzle- 78 mm ( original type 130 mm) the distribution of gas bubble is relatively uniform

it is available to improve flow field and inclusions floating off. The results of pilot commercial production of 180 mm x 700 mm cast slab show that the amount of ≥30 μm inclusions and total amount of inclusions in ultra-low carbon steel with using optimizing parameters decrease obviously.